The invention relates to a process for the application of a coating to at least a part of the exterior surface of glass containers, an apparatus for the application of a coating to at least a part of the exterior surface of glass containers and a glass container comprising a coating of plastics material extending at least over a part of its exterior surface.
In one known process for applying a coating to glass containers disclosed in EP 0 442 735 A2 numerous gripping devices are conveyed on a continuously circulating endless conveyor through a coating installation. Each gripping device grips a row of glass containers arranged transversely to the direction of conveyance at a pick-up site, guides the row upwards at an angle, and then downwards at an angle, with the result that the row is dipped into a bath of liquid coating material and subsequently is directed upwards again at an angle to an upper level. At this level the row passes through a bottle base setting zone, and is thereafter guided downwards at an angle and deposited on a conveyor belt. On the conveyor belt the row passes through a setting zone in order to harden the parts of the coating on the glass containers which have not yet been hardened. The emptied gripping devices are conveyed back to the pick-up site on the return run of the endless conveyor. All the devices are fixedly mounted on the endless conveyor and therefore each moves always with the same velocity.
Also, from WO 94/17002 A1 it is known to guide numerous gripping devices on an endless conveyor through the coating installation. Each gripping device picks up from the lehr conveyor a row of glass containers arranged transversely to the direction of transportation. Each row is moved upwards at an angle, then downwards at an angle and dips into a bath of liquid coating material, and then after leaving the bath is guided initially on an upwardly sloping and then downwardly sloping path through a zone for the thermal ageing of the dip overlay, and thenxe2x80x94again in sloping upward and downward movementsxe2x80x94passes through a setting zone, and finally is again deposited on the lehr conveyor. Each gripping device comprises two gripping bars which respectively engage all the glass containers of the relevant group on opposing sides below the neck. The two gripping bars are opened or closed synchronously by a plurality of drive devices distributed over their length. Each drive device comprises a cylinder mounted on a base portion and part of a piston-cylinder unit whose piston rod carries at the lower free end, and parallel to the gripping bars, a rod which is guided in vertical slots of the base portion. Actuating arms of the gripping bars extend transversely to a longitudinal axis of the gripping bars and are each mounted on the rod to be pivotable upwards and downwards with an elongate hole about an axis of the base portion. Here again all the gripping devices circulate all with the same velocity.
From DE 26 55 411 A1 there is known another type of coating process. Here, a plurality of carriages are drivable independently of one another in a transportation plane on rail segments. Each carriage comprises a plurality of gripping units transversely to a direction of transportation. In a first gap between rail segments a holder picks up an empty carriage and pivots it downwards towards a pick-up site of a tempering device for bottles arranged in rows. There, the gripping units of the carriage grip a row of bottles. The holder is pivoted upwards together with the filled carriage in the first gap. From there, the carriage is caused to travel by way of a rail segment into a lifting mechanism which is waiting in a second gap. The lifting mechanism, together with the carriage, is lowered in the vertical direction until the bottles dip into a fluidized bed of thermoplastic powder. As soon as sufficient powder adheres to the bottles, the lifting mechanism is raised and the carriage with the coated row of bottles is displaced on a rail segment in the second gap. On this rail segment the carriage together with the row of bottles travels successively through a heating chamber, a ventilation chamber and a spray quenching chamber. Thereafter, the row of bottles is deposited at a delivery station by deactivation of the gripping units.
From the German published patent application 2 219 470 another coating process is known per se. Holders for respective individual bottles can be raised and lowered about a horizontal axis at intervals on a chain conveyor. The bottles are pre-heated in a raised position, then are lowered into a fluidized bed of plastics particles, and then are moved again in raised position through a melting oven.
From U.S. Pat. No. 4,022,155 A and German published patent application 2 310 923 it is known per se to swivel glass containers with a parallelogram-type handling device by gripping devices from a first conveyor belt through a coating station and after the coating process onto a second conveyor belt. The coating station comprises a fluidized bed into which the containers are dipped. The fluidized bed contains a thermoplastic polymer.
From US 3 270 710 A it is known per se to coat a glass bottle first with a liquid primer and then with a liquid vinyl resin.
From US 3 200 002 A it is known per se to coat bottles in a dipping process with a liquid plastisol, and for this to move gripping devices continuously with an endless conveyor chain.
From DE 26 17 976 B2 a special bell-shaped gripping unit is known per se. A longitudinally slotted spring sleeve is (guided displaceably by means of a piston within a closed outer bell. On each tongue of the spring sleeve there is located at the bottom a gripping claw which is moved radially inwards into positive contact with the glass container by means of an abrasion-resistant ring upon axial relative movement between spring sleeve and bell. A plug which is connected rigidly to the bell is in contact with the top of the mouth or the closure of the glass container. A compression spring biasses the gripping claws into their gripping position. The gripping claws are guided by compressed air into their release position. The compressed air acts on the upper side of the piston of the spring sleeve.
From DE 24 31 952 C2 there is known per se a process for protecting glass bottles from shattering by the application of a plastics coating, in which the glass bottles are coated with a coating powder of softened duroplastic resin by dipping into a fluidized bed or an electrostatic fluidized bed, and the resin deposited to a thickness of at least 50 xcexcm is thermally cured. In this way a coating is created which offers a good resistance to shattering as well as good strength and resistance to alkalis as well as having small frictional resistance, so that one thereby has a smooth transparent exterior surface as well as a product which is economical to manufacture.
The solution known from DE 25 10 734 B2 concerns a process for the coating of glass bottles with a transparent, duroplastic protective layer by the application of powdered lacquer in a fluidized bed or in an electrostatic fluidized bed. Primarily, one is talking here about pure glass bottles with an aqueous or alcoholic silane finish, dried and heated. The applied protective layer is very elastic, has excellent adhesion and resistance to alkalis and ensures a longer period of utilization for use as a multiple-use bottle.
From DE 27 48 696 A1 there is known a process for the coating of hollow glass bodies, in which a duroplastic powder varnish is used which is applied in a fluidized bed.
It is the object of the invention to improve the coating of the glass containers and to improve the coated glass containers themselves.
This object is achieved, in respect of the process, by
(a) bringing the glass containers to a temperature suitable for the coating process;
(b) gripping a group of the glass containers at a pick up site with a gripping device, temporarily sealing the openings in the containers, raising the group of glass containers in a substantially vertical direction to a first level above the pick up site, moving the group of glass containers horizontally to a position above a vessel containing a coating medium, lowering the group of glass containers in a substantially vertical direction into the coating medium to a second level and maintaining the glass containers therein until sufficient the coating medium adheres thereto;
(c) raising the group of glass containers substantially vertically from the second level to a third level and then moving the group substantially horizontally;
(d) unsealing the openings in the containers and transferring the group of glass containers onto a conveyor by releasing the containers from the first gripping device;
(e) moving the group of containers on the conveyor through a setting zone wherein at least a part of the coating medium adhered to the group of containers hardens; and
(f) returning the first gripping device to grip a second group of glass containers.
By this means the handling device can be simplified-and a trouble-free transportation of the glass containers is facilitated. Preferably, each group of glass containers is taken from the lehr conveyor of a lehr furnace which follows a glass forming machine. This permits the inherent thermal energy of the glass containers at the end of the lehr furnace to be utilized to the optimum, so that the coating medium is applied to the optimally tempered glass containers and subsequently hardens to a resistant protective layer. Preferably, the group is entrained in the direction of transportation of the lehr conveyor during the pick-up from the continually circulating lehr conveyor, and then is transferred to the vertical direction of movement. In this way the glass containers can be picked up smoothly and swiftly. The gripping devices are uncoupled from one another and can be moved on each section of the path with optimum velocity profile. This contributes well to the quality of the coating and consequently to the quality of the glass containers. The dipping time of the glass containers in the coating medium which is important for a uniform andxe2x80x94to save coating mediumxe2x80x94as thin as possible formation of the layer can be maintained very accurately.
Through the steps of moving the group of glass containers at the third level to above a set-down plate prior to the step of hardening the coating medium on the bases, lowering the group of glass containers onto the set-down plate, depositing the group of glass containers onto the set-down plate by releasing the containers from the first gripping device and then returning the first gripping device in accordance with step (f), subsequently gripping the group of glass containers on the set-down plate with a second movable gripping device, raising the group of containers back to the third level and moving the group of glass containers substantially horizontally to the base setting zone the carry-over of residual coating medium beyond the set-down plate can be substantially reduced or eliminated.
By moving the group of glass containers in step (c) at the third level to a position directly above the conveyor one has a particularly rapid and cost-effective manner of operation.
If the layer is to be set first on the bottom of the glass containers, before the glass containers are deposited on the conveyor belt it is recommended to provide a base setting zone for hardening the coating on the bases of the group of glass containers. The group of glass containers at the third level may then be moved to the base setting zone after the step of raising the group of glass containers from the second level and the coating medium on each of the bases of the group of glass containers at said base setting zone may then be hardened. The group of glass containers at the third level is then moved from the base setting zone to the position directly above the conveyor.
An overall favorable motion characteristic for the glass containers is achieved by including in step (f) the steps of moving the first gripping device substantially horizontally at a fourth level into a position above the pick up site and subsequently lowering the first gripping device down substantially vertically to the pick up site.
A service station may be visited by the gripping device either in each operating cycle or only as needed. Preferably this is accomplished as part of step (f) by including the steps of moving the first gripping device at a fourth level to a service station and servicing the first gripping device by performing steps including cooling the first gripping device, cleaning the first gripping device, discharging rejected glass containers from the first gripping device and/or replacing the first gripping device with a replacement first gripping device, and then moving the first gripping device at a fourth level substantially horizontally into a position above the pick up site and subsequentially lowering the first gripping device substantially vertically to the pick up site.
By making the fourth level the same as the first level a structural and operational simplification is achieved.
A rapid exchange of the containers is possible even within the normal operating cycle if, when the vessel holding the coating medium is in need of service, it is moved out from its operational position transversely to the direction of transportation of the glass containers and is replaced by an operationally ready reserve vessel.
Preferably other gripping devices are moved in a separate closed path as part of step (d), wherein the other gripping devices are emptied of glass containers and then conveyed back to the set-down plate in order to pick up another group of the glass containers.
Preferably, a bottom hardening takes place with the glass containers stationary. A heating by thermal radiation can be effected not only from below, but at any suitable angular orientation of a heating arrangement relative to the bottom of the containers.
Following the base setting zone the glass containers are cooled and can be sprayed with a friction-reducing liquid solution in a cold-end coating process known per se.
By lowering the glass containers into a fluidized sinter bed containing a powder as a coating medium in step (b) one has a uniform and easily controllable coating process. Alternatively, the powder could be applied to the glass containers by an electrostatic coating process known per se.
Preferably the powder comprises hardenable resins and a hardener component, and is hardened at least to an approximately duroplastic coating on the glass containers resulting in a particularly favorable coating of the glass containers. Glass containers made in this way are suitable to take filling products under increased internal pressure, for example drinks containing carbon dioxide. Preferably, powder having a grain size of 5 to 60 xcexcm is used.
A particularly smooth exterior surface of the coating is achieved by including a dispersion coating medium in the vessel into which the glass containers are lowered in step (b) and by using acrylic resins in the dispersion as a dispersed phase, the resins being hardened to an acrylic resin lacquer coating on the glass containers.
The aforementioned object of the invention is achieved by an apparatus including a temperature adjusting device for bringing a group of the glass containers to a temperature suitable for the coating process; a pick up site and a path extending from the pick up site; a handling device which includes the first movable gripping device capable of gripping the group of glass containers at the pick up site and moving them therefrom and returning to the pick up site after releasing the group of glass containers, the first gripping device having a carrier movable along the path and a plurality of gripping units arranged on the carrier, there being one gripping unit for each of the glass containers of the group, each gripping unit comprising a base portion, a longitudinal axis, and at least three gripping elements movably mounted thereon and moveable between a gripping position gripping one of the glass containers and a release position releasing the one glass container, each of the gripping elements comprising an actuating arm extending toward the longitudinal axis of the gripping unit, each the gripping unit further comprising a piston-cylinder unit for actuating the gripping elements between the gripping and releasing positions; a vessel disposed along the path for containing a coating medium, the vessel positioned to receive the group of glass containers, the handling device capable of dipping the group of containers into the coating medium and raising the group of containers therefrom and moving the group of containers onward; a setting zone for hardening at least a part of the coating medium coating the glass containers, the setting zone disposed along the path; and a conveyor traversing the setting zone for receiving the group of glass containers released from the gripping device and conveying the glass containers through the setting zone. As tempering device one can use for example the lehr oven which follows a glass molding machine. Before the pick-up by the gripping device, the glass containers can be completely uncoated or be provided just with a hot-end coating known per se. In particular, the carrier can be made substantially rectangular. The group is then for example a rectangular matrix of 15 rows and 40 columns, thus a total of 600 glass containers, with all the glass containers being arranged spaced from one another. The group can be simply and reliably set down on the conveyor belt after the coating process. The setting of the coating on the conveyor belt is effected particularly uniformly and is easily controllable. As necessary, the base setting zone for the base coating of the glass containers is provided if it appears necessary to carry out such base setting in advance before the glass containers are deposited on the conveyor belt. Each gripping unit is preferably provided with four gripping elements. This gives the possibility, with an arrangement of the gripping units in a predetermined matrix, of moving the gripping elements with minimum spacing of the gripping units from one another into suitable intermediate spaces between the gripping units. The piston-cylinder unit is preferably double-acting and is actuated pneumatically. Instead of an upward and downward pivoting of the gripping elements, these could alternatively be actuated in such a manner that they are moved linearly in relation to the rest of the gripping unit.
To ensure that substantially no coating medium adheres to the first gripping device, which medium could otherwise harden in particular in a base setting zone and contaminate the gripping device and adversely affect its function, the apparatus includes a set-down plate disposed to receive the group of glass containers deposited thereon from the first gripping device and a second handling device having a second gripping device movable along the path through the base setting zone for gripping and moving the group of glass containers from the set-down plate through the base setting zone to the conveyor, the second gripping device being movable back to the set-down plate for gripping a further group of glass containers after depositing the group of glass containers on the conveyor.
The coating medium is prevented from getting into the interior space of the gripping elements in the gripping position because each gripping element comprises a segmental form and sealingly cooperates in the gripping position with the other gripping elements of the gripping unit and with the glass container gripped by the gripping elements to sealingly cover a gripped portion of the gripped glass container.
The gripping elements can be particularly easily moved and in a functionally reliable way because the piston cylinder unit preferably comprises a main cylinder arranged concentrically within the base portion. The main cylinder has a bore arranged coaxially with a piston arranged concentrically and displaceably within the cylinder. A piston rod extends from the piston concentrically through the bore. Actuating arms are coupled to the piston rod.
A spring, arranged between the piston and the base portion for biasing the gripping elements into a gripping position ensures that, in the absence of pressurized medium, the gripping elements are closed into their gripping position.
By using a main cylinder securable to the carrier and forming a cylinder chamber, the cylinder having a base portion comprising an upper piston portion displaceably and sealingly guided in the main cylinder, it is possible to balance the gripping unit for the case where the mouth of a glass container is arranged eccentrically to an otherwise impermissible degree and thereby ensure that an opened gripping element strikes against the mouth of the container upon lowering of the gripping unit.
A biasing spring, arranged between the upper piston portion and the main cylinder biases the upper piston portion into a lowermost position, thereby ensuring that the gripping unit is continuously biased into the normal operating position.
The carrier includes an elongated longitudinal slot adjacent to the base portion. The base portion includes a pin extending therefrom and engaging the slot. The pin and slot thereby secure the base portion against rotational motion relative to said carrier thereby providing a particularly simple safety against rotation.
The elongated slot forms part of a bayonet link allowing the gripping unit to be exchanged rapidly, as necessary.
Preferably the piston rod has a concentric aperture through which extends a second piston rod having a free upper end securable to the base portion of the cylinder. The lower end of the second piston rod carries a second piston positioned at the level of the gripping elements. An additional cylinder is displacably guided on the second piston and piston rod. The additional cylinder carries a stop at the bottom which cooperates sealingly, either with a mouth of a glass container or with the gripping element when they are located in their gripping position. These features fulfil a double function. On the one hand, in normal operation the mouth of the glass container is sealed off by the plug, and thus an undesirable penetration of coating medium into the glass container is prevented, and on the other hand the plug seals off the lower gripping aperture of the gripping elements when located in the gripping position if no glass container should be located below this gripping unit on any occasion. Thus, again, in the latter case, coating medium is prevented from getting into the interior of the gripping unit.
Between the additional cylinder and the second piston rod a spring is arranged which biases the plug into a lowermost position to ensure that the plug can fulfill its function even in the absence of the relevant pressurized medium.
The pressurized medium is preferably compressed air at, for example 3 bar, which is conducted through a hollow chamber extending in the second piston rod in order to raise the additional cylinder.
Air at a pressure of, for example, 4900 Pa (500 mm water head) is used as flushing gas. The flushing gas is introduced into the cylinder chamber and conducted through channels in the upper piston portion into a concentric through aperture of the piston rod and from there into an internal chamber of the gripping elements. The flushing gas on the one hand cools the gripping unit and prevents or reduces in this way the tendency of coating medium to stick to the gripping unit. Additionally, by means of the flushing gas, an excess pressure is created in the interior space of the gripping unit, with the result that the penetration of coating medium into the gripping unit is made more difficult or is prevented.
Preferably the supply of pressurized medium is effected by a common supply device which permits structural and operational simplification. Each supply device comprises a plurality of pipes separate from one another, one of the pipes being connected permanently connected to the cylinder chamber and each one of the remaining pipes being connected to an associated aperture in a side wall of the main cylinder. In terms of the number of gripping units one is talking here preferably about several gripping units of a column in the predetermined matrix. Such a column comprises for example 15 gripping units arranged spaced from one another.
Each supply device is sealingly connectable with an end wall of the associated plurality of gripping units and each pipe is connected by means of a connecting bore of the supply device permanently to a terminal channel of the main cylinder, each terminal channel issuing into an association aperture.
Because the gripping elements project in their gripping position in the radial direction on all sides with an overhang beyond the associated container, coating medium possibly falling from the gripping elements is prevented from falling onto the glass containers suspended by the gripping elements, which could otherwise lead to a non-uniform coating.
By arranging each group of the glass containers to be dipped simultaneously into at least one vessel containing the coating medium, and having each vessel containing a fluidized sinter bed comprising a powder as a coating medium one achieves a particularly uniform and economical coating. More than one vessel can be used if the operational circumstances require this.
Preferably each vessel, starting at its base, comprises, in sequence, an air chamber, a porous plate and a dispersing device movable in the powder. This ensures a reliable coating operation. The air chamber is preferably divided into cells in order to ensure that the air supply over the cross sectional surface area of the fluidized bed is as uniform as possible. The porous plate is of such porosity that the air is able to travel upwards from below, but that powder particles cannot pass through the plate. The porous plate is made for example as a bronze or plastics sintered plate.
A cullet basket, arranged above the dispersing device and which can be raised from the powder, ensures that glass containers or cullet which has fallen into the fluidized bed can be removed easily again from the fluidized bed.
By arranging a suction channel open towards the fluidized bed along the upper edge of each vessel ensures that the surroundings of the vessel can be maintained free from the residual powder in an effective way.
By arranging each group of the glass containers to be dipped simultaneously into at least one vessel containing a dispersion as coating medium constructional simplifications in comparison to using powder as coating medium is achieved.
To obtain certain operational advantages a sensor device is provided by means of which one may ascertain whether and how many gripping units of the gripping device have gripped no glass container. The drive means of the handling device is controllable dependent upon the number of glass containers which are not gripped so that the gripping units always dip into the coating medium to at least the same depth. The dipping depth of the gripping units should be kept as small as possible, so that as little coating medium as possible sticks to the gripping units and can pass into the glass containers and the surroundings.
The drive means of the handling device is controllable so that the speeds at which the glass containers are dipped into the coating medium and raised from the coating medium are modulated such that there results a particularly rapid and reliable coating. For example, the velocity can be kept constant on the one hand when dipping the glass containers, shortly before the contact of the surface of the coating medium by the base of the glass containers, and on the other hand when raising the glass containers shortly before the bases of the containers rise again from the surface. In particular, this should prevent coating medium from being excessively agitated and distributed in an uncontrolled manner into the surroundings by the dipping and raising movements of the glass containers and of the gripping units.
By providing the set-down plate with apertures therethrough and connecting an underside of the set-down plate to a chamber in which a reduced pressure can be created residues of the coating medium can be collected and possibly returned to the process.
Preferably the base setting zone includes a heating register having a heating device facing the base of each glass container. The heating device can be for example an electrical resistance heater with a circular heating plate or it can be formed as an annular gas burner.
So that heat energy is spared, and an undesirable heating of the relevant gripping units can be reduced those heating devices which are arranged opposite places where glass containers are absent are arranged to be rendered inactive.
If the base coating has not set before the glass containers are set down on the conveyor belt then it is preferred that the conveyor belt has comparatively small and numerous support zones which come into contact with the coated bases of the glass containers. The conveyor belt can be made for example similar to a wire mesh.
By providing a separating means to at least the support zones of the conveyor belt before the bases are set down on the support zones sticking of the bases of the glass containers to the conveyor belt can be prevented or greatly reduced. The separating means can for example be sprayed on to the conveyor belt as a liquid.
Better utilization of space and protection against uncontrollable tipping over of glass containers is achieved if, in each group of the glass containers leaving the temperature device, the glass containers are arranged in a direction of conveyance in columns and transversely to the direction of conveyance in rows wherein the adjacent columns and rows each are offset relative to one another, preferably by a half spacing. Preferably, each glass container of each group has the same size spacing form all adjacent glass containers of the group.
The aforementioned object of the invention is achieved in respect of the glass container itself by a glass container comprising a coating of plastics material extending at least over part of its exterior surface, the coating being produced by the process and apparatus as described above, and wherein the ratio V, which equals the ratio of the glass mass of a glass container coated according to the invention to the glass mass of a glass container according to the prior art having the same filling volume and the same filled product but uncoated or provided only with a hot-end coating and a cold end coating is between 0.62 to 0.86. By these means it is possible significantly to reduce the glass mass and consequently the wall thickness of the glass containers as compared with the prior art. Any such reduction leads to considerable economical advantages. The thickness of the coating can be 30 to 60 xcexcm.
Preferably the coating comprises duroplastic powder lacquer, wherein the powder lacquer coating can, as required, be glossy, transparent, smooth, glass-clear, colored, or be formed in some other way. The duroplastic powder lacquer layer represents excellent protection against damage to the exterior surface of the glass. Thus, it is possible to preserve the strength of the glass during use of the glass containers.
Substantially the same advantages and, in addition, a particularly smooth exterior surface of the coating results if the coating is an acrylic resin lacquer obtained from a dispersion.
The possible savings in glass mass which can be achieved with examples of glass containers available on the market range between a V of 0.62 to a V of 0.86.
These and other features and advantages of the invention will now be described in more detail with reference to embodiments which are given by way of example and which are shown in the drawings.